Various chemical treatments exist for glass-type surfaces such as glass fibers to aid in their processability and applications. Before bundling the filaments together after formation, a coating composition or sizing composition is applied to at least a portion of the surface of the individual filaments to protect them from abrasion and to assist in processing. As used herein, the terms “sizing composition,” “sizing,” “binder composition,” “binder,” or “size” refer to a coating composition applied to the filaments immediately after forming. Sizing compositions may provide protection through subsequent processing steps, such as those where the fibers pass by contact points as in the winding of the fibers and strands onto a forming package, drying the aqueous-based or solvent-based sizing composition to remove the water or solvent, twisting from one package to a bobbin, beaming to place the yarn onto very large packages ordinarily used as the warp in a fabric, chopping in a wet or dry condition, roving into larger bundles or groups of strands, unwinding for use as a reinforcement, and other downstream processes.
In addition, sizing compositions can play a dual role when placed on fibers that reinforce polymeric matrices in the production of fiber-reinforced plastics. In such applications, the sizing composition provides protection and also can provide compatibility between the fiber and the matrix polymer or resin. For instance, glass fibers in the forms of both woven and nonwoven fabrics and mats and rovings and chopped strands have been used with resins, such as thermosetting and thermoplastic resins, for impregnation by, encapsulation by, or reinforcement of the resin. In such applications, it is desirable to maximize the compatibility between the surface and the polymeric resin while also improving the ease of processability and manufacturability. It would be desirable to provide a sizing composition for glass fibers that is compatible with a wide variety of thermosetting and thermoplastic resins and that can also be processed and manufactured well.
An example of a resin is a vinyl addition polymer like polyvinyl chloride (PVC). In selecting a sizing composition for use with PVC powders, plastisols, or organosols, fiber glass manufacturers have struggled with the PVC compatibility, coating performance, and weaving defects. Another problem area has been broken filaments. For example, broken filaments can accumulate in the creel guide-eyes and in the PVC plastisol itself, as well as in the coater dies. Excessive accumulation can result in a breakout and/or a loss of productivity. Thus, it would be desirable to provide a fiber glass product coated with a sizing composition that performs well and improves productivity by generating minimal broken filaments.
In the past, fiber glass strands coated with starch-oil based sizing compositions have been used in PVC coating applications. U.S. Pat. No. 5,466,528 provides an example of such a sizing composition. However, fiber glass products coated with such starch-oil based sizing compositions have experienced broken filament issues. It would be desirable to provide a sizing composition that performs well in PVC coating applications without significant performance issues.
Rosins have been previously disclosed as part of coating compositions for fiber strands. Some of these prior disclosures may not utilize rosins in amounts that would realize the desirable attributes that such rosins can provide when coated on fiber glass as part of a sizing composition. Such desirable attributes are discussed in more detail below in connection with the discussion of the present invention. Other disclosures utilize rosins as part of coating compositions that would not be suitable for the applications contemplated by the present invention due to properties of the fiber glass coated with such coating compositions.
It would be desirable to provide fiber glass strands coated with a sizing composition that are compatible with a wide variety of resins for encapsulation, impregnation, reinforcement, or coating, where the compatibility is good enough to be an improvement over that obtained with starch-oil type formulations and where the processability of the fiber glass strands before and after use with the resin results in a reduction in defects.